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Introduction to Basic Concepts in Ophthalmology

Overview of the Review Session

• The speaker introduces a review session focusing on essential concepts in ophthalmology, emphasizing important topics for an upcoming exam.

• The method of studying involves asking questions among peers to identify correct answers and areas needing improvement.

Understanding Visual Acuity

• The definition of 20/20 vision is discussed: the ability to discern two points clearly at 20 feet, indicating normal visual acuity.

• A person with 20/200 vision can see what a normal person sees at 20 feet from a distance of 200 feet, illustrating poorer vision as numbers increase.

Visual Acuity Measurements

• Larger numbers indicate worse vision; for example, road signs often use sizes like 20/400, which should be readable by someone with normal eyesight at 400 meters.

• The "Bell's sign" is introduced, where eyes move upward and outward involuntarily when attempting to close them due to facial paralysis.

Clinical Examination Techniques

Clinical History and Instruments

• Discussion includes clinical history taking and instruments used for eye examinations as part of medical semiology.

Snellen Chart and Visual Acuity Testing

• The Snellen chart is mentioned as a tool for measuring visual acuity; it helps determine how well individuals can see letters at specified distances.

• Definitions include that clear contours must be separated by a minimum distance of 1.75 mm on the chart.

Understanding Vision Correction

Pinhole Test

• The pinhole test is explained as a method that allows light rays to enter more directly into the eye, helping assess if poor vision is due to refractive errors requiring glasses.

Presbyopia Explained

• Presbyopia or "farsightedness" occurs when aging reduces lens elasticity, making it difficult for individuals to focus on nearby objects without moving them further away.

Anatomy of the Eye

Structure Comparison

Understanding the Eye's Lens System and Accommodation

Anatomy of the Eye's Lens System

• The anterior part of the eye, known as the anterior chamber, consists of the cornea and lens. The cornea has an average power of 44 diopters, while the lens typically has a power of 20 diopters.

• The cornea acts solely as a lens without any additional functions, whereas the lens (cristalino) is connected to fibers called zonules that help in focusing.

Mechanism of Accommodation

• When viewing distant objects, the ciliary muscles relax, allowing the lens to maintain its relaxed shape for clear vision. Conversely, when focusing on nearby objects, these muscles contract to change the shape of the lens for better focus.

• As people age, their lenses lose flexibility and become rigid, making it difficult to focus on close objects—a condition known as presbyopia that affects everyone eventually. This process is similar to developing wrinkles or gray hair over time.

Visual Impairment and Correction

• Individuals over 40 often struggle with near vision due to decreased accommodation ability; they may need reading glasses (lentes de lectura) for small text clarity. This issue arises not from excessive use but from natural aging processes affecting lens elasticity.

• Reading glasses are available in various strengths starting from +1 at age 40 up to +3 by age 60 due to increasing difficulty in focusing on close objects as one ages. These adjustments are necessary for maintaining clear vision at different distances.

Refraction and Vision Testing

• Refraction refers to how light waves change direction when passing through different media; this principle is used in creating corrective lenses based on individual needs determined during eye exams using devices like retinoscopes or autorefractors.

• Myopia (nearsightedness) occurs with negative sphere values while hyperopia (farsightedness) corresponds with positive values; astigmatism is indicated by cylindrical measurements on prescriptions which help tailor lenses accordingly.

Presbyopia: A Common Age-related Condition

Understanding Refractive Surgery and Vision Changes

The Impact of Age on Vision

• Young individuals typically have clear vision due to the flexibility of their lens, allowing them to focus well on small text.

• Presbyopia, a condition where near vision diminishes, usually begins around age 40; thus, younger patients are ideal candidates for refractive surgery.

• If a patient over 50 is operated on for distance vision correction without addressing presbyopia, they will still struggle with near vision.

Candidate Selection for Refractive Surgery

• Ideal candidates for refractive surgery are generally in their 20s since they have many years before developing presbyopia.

Understanding Astigmatism

• Astigmatism arises from an irregularly shaped cornea and is corrected using cylindrical lenses that align with the cornea's curvature.

• A normal cornea is spherical, while an astigmatic cornea resembles an oval shape (like a football), necessitating specific lens adjustments.

Myopia vs. Hyperopia

• In myopia (nearsightedness), light rays focus before reaching the retina; hyperopia (farsightedness) occurs when they focus behind it.

• Generally, larger eyes tend to be myopic while smaller eyes may be hyperopic; however, astigmatism can occur regardless of eye size.

Surgical Considerations in Ophthalmology

• There’s a belief that aspiring ophthalmologists should avoid laser surgery to correct myopia during training; however, many do undergo this procedure during residency.

• The safety and feasibility of laser surgery depend on the thickness of the cornea and degree of refractive error; excessive thinning can lead to complications like keratoconus.

Procedure Insights

Corneal Surgery Insights

Overview of the Surgical Procedure

• The surgical tool, referred to as "navajita," is used for making incisions. The process involves moving the blade forward to create a cut.

• After cutting, the suction is released, allowing the flap of the cornea to be lifted. This exposes the stroma where laser adjustments are made according to the patient's prescription.

• The entire procedure typically lasts under 20 minutes and can be performed on both eyes. Post-surgery, patients may experience dry eyes.

Importance of Precision in Surgery

• It’s crucial that measurements and procedures are executed with precision since any errors could lead to lifelong vision issues due to incorrect laser settings.

• Complications such as regression into myopia can occur post-surgery; patients often report returning to glasses after initially successful surgery.

Corneal Thickness Considerations

• Proper measurement of corneal thickness is essential before surgery; it must remain thick enough post-procedure to maintain stability and prevent complications like myopia recurrence.

• There isn't a specific percentage for complications; outcomes depend heavily on initial conditions and surgical execution.

Patient Eligibility and Alternatives

• Patients with insufficient corneal thickness should not undergo this type of surgery but may consider alternative safer options available.

Post-Surgical Support and Resources

• The speaker offers support for those interested in surgery in Mexico City, encouraging potential patients to reach out for assistance or discounts.

Understanding Keratoconus

Corneal Measurements and Conditions

• Keratometry measures corneal curvature; irregularities can indicate astigmatism which complicates surgical candidacy.

• Normal corneas measure between 500 - 550 microns; deviations from this range can lead to structural issues like keratoconus.

Effects of Corneal Thinning

• When parts of the cornea thin excessively, they lose shape leading to conditions like keratoconus, which cannot be treated with refractive surgery.

Intraocular Pressure Measurement Techniques

Tools Used in Ophthalmology

• Intraocular pressure (IOP), measured between 10 - 21 mmHg using specialized devices, is critical for assessing eye health.

Examination Techniques

• Various optical tools allow examination at different depths within the eye, including assessments of cataracts and other ocular structures.

Ocular Examination and Conditions

Eye Alignment and Deviation Tests

• The light must fall centrally between the pupils; deviations indicate misalignment. One patient shows inward deviation, while another exhibits outward deviation.

• The Hirshberg test assesses eye alignment, while Bell's sign indicates corneal protection reflex when closing the eye, preventing dryness.

Diagnostic Laboratory Tests

• Suggested tests include glycosylated hemoglobin for diabetes, antinuclear antibodies for autoimmune conditions, and HLA B27 for ankylosing spondylitis. Thyroid disease may also be indicated through ocular symptoms.

Visual Field Testing

• Campimetry evaluates retinal function; normal visual fields contrast with those affected by glaucoma, where peripheral vision is lost.

• Optical Coherence Tomography (OCT) examines retinal layers; a healthy macula should not show fluid or edema.

Ptosis: Definition and Types

• Ptosis refers to drooping of the upper eyelid; a decrease of more than 2 mm is clinically significant.

• Mild ptosis is defined as a drop of 2 mm or more in the upper eyelid.

Causes and Classifications of Ptosis

• Ptosis can be congenital (present at birth), such as simple ptosis or associated with syndromes like blepharophimosis. Acquired forms include neurogenic, myogenic, aponeurotic, and mechanical causes.

• Neurogenic causes often involve cranial nerve paralysis (e.g., third cranial nerve palsy), while mechanical causes may arise from tumors or trauma affecting eyelid mobility.

Specific Conditions Related to Eyelids

• Myogenic ptosis includes conditions like myasthenia gravis. Congenital cases often present with compensatory head positioning due to limited eyelid elevation.

• Mechanical ptosis results from excess skin or tumors obstructing full eyelid elevation. Triquiasis involves misdirected eyelashes that irritate the eye surface.

Understanding Eyelid Conditions and Treatments

Eyelid Tension and Entropion

• The lower eyelid can lose tension, causing it to protrude outward. In contrast, entropion is when the eyelid turns inward, which can lead to corneal damage due to eyelashes rubbing against the eye.

Chalazion vs. Stye

• A chalazion is a chronic condition where a cyst forms in the eyelid without inflammation, while a stye (or hordeolum) is an acute inflammatory response that is painful and swollen.

• Treatment for a stye may include antibiotics and anti-inflammatory measures, whereas a chalazion typically requires surgical drainage since it does not respond to standard treatments.

Blepharitis Overview

• Blepharitis refers to chronic inflammation of the eyelid margins. It is often associated with Staphylococcus bacteria.

Dacryocystitis Explained

• Dacryocystitis involves inflammation of the lacrimal sac, often due to obstruction (stenosis). This condition can lead to infection if not treated properly.

Treatment Approaches for Lacrimal Obstruction

• Stenosis indicates narrowing or blockage of the tear duct system. Initial treatment may involve conservative methods like massage before considering surgery.

• If conservative measures fail after one year of age, intubation may be performed using a tube that connects the tear duct to the nasal cavity.

Ocular Motility and Strabismus

Eye Muscle Innervation

• All eye muscles are innervated by cranial nerve III except for the fourth (trochlear nerve) and sixth (abducens nerve), which control specific muscle movements.

Identifying Eye Deviations

• Understanding muscle paralysis helps identify deviations; for instance, if one eye moves towards its stronger muscle while another does not move as expected, it indicates paralysis in that muscle.

Epicantal Folds and Strabismus

• Epicantal folds can create an illusion of strabismus in children; however, true strabismus involves misalignment where light falls off-center on the pupil.

Amblyopia: Causes and Associations

Definition and Implications

• Amblyopia refers to reduced visual acuity without any identifiable organic cause. It’s commonly linked with strabismus but can also arise from differences in refractive error between eyes or congenital issues like cataracts or retinoblastoma.

Conjunctivitis Differentiation

Understanding Conjunctivitis

Conjunctivitis: Types and Characteristics

Bacterial Conjunctivitis

• Bacterial conjunctivitis is characterized by purulent exudate, which appears yellowish-green. This type often results from contact between the eye and contaminated hands.

• Common symptoms include redness, a sensation of a foreign body in the eye, and tearing. The most prevalent bacteria involved are Staphylococcus species.

Viral Conjunctivitis

• Viral conjunctivitis typically presents with a more watery (serous) discharge and may be associated with respiratory illnesses or exanthematous diseases.

• Adenoviral infections can lead to follicular conjunctivitis, where infiltrates may also be present. Symptoms include abundant tearing but minimal discharge.

Allergic Conjunctivitis

• Allergic conjunctivitis is marked by the presence of papillae on the conjunctiva, significant itching, and redness. It often occurs due to contact with allergens.

• Papillae are round structures that differ from follicles; they appear as raised bumps while follicles are smaller and more pointed.

Differentiating Features

• Histologically, papillae have a central vascular tuft while follicles have marginal vessels that are more superficial. This distinction aids in clinical diagnosis.

• Understanding these differences is crucial for effective treatment strategies tailored to each type of conjunctivitis.

Treatment Overview

• Bacterial infections are treated with antibiotics such as penicillin for gonococcal infections or tetracyclines for chlamydial infections like inclusion conjunctivitis.